Identifiable synthetic polymeric materials containing gold,indium and/or lanthanum



United States Patent 3,439,168 IDENTIFIABLE SYNTHETIC POLYMERIC MA- TERIALS CONTAINING GOLD, INDIUM AND/OR LANTHANUM Charles H. Lindsley, Asheville, NC, assignor to American Enka Corporation, Erika, N.C., a corporation of Delaware No Drawing. Filed Aug. 10, 1964, Ser. No. 388,671 Int. Cl. G21h 5/02; H013 39/26 US. Cl. 250-106 5 Claims ABSTRACT OF THE DISCLOSURE The present invention relates to a new and efficient method for tagging materials, particularly synthetic polymeric materials, the products produced thereby, and to a unique and novel technique for identifying the tagged materials.

The use of trademarks, whether in the form of names, designs, symbols or the like, to identify the goods is, of course, very well known. The purpose of such marks is to make known the source of the goods to the public. Often it is not feasible to mark the goods in the conventional manner, and in these instances the mark or marks may be applied to the package containing the goods or to a label or other tag applied to the goods. As examples of such materials, mention may be made of granular or powdered products, yarns, filaments, liquid materials, and the like. in other situations, the manufacturer or producer of the goods may wish to mark the goods so that he may be able to identify them after they left his control and/or have been in commerce without, however, placing the usual'markings indicating the source thereof.

Heretofore, products have been made which have incorporated therein a substance by which the manufacturer can make known to the public his particular product or products. Patents 2,256,549, 2,390,512, and 2,753,272 disclose the addition of various elements and compounds to cellulosic fibers as a means of identification of the fibers for manufacturing purposes. These patents contemplate addition of fairly large amounts of the identifying material which can involve a large expense when the identifying substance is costly.

Additionally, unwanted elfects may be incorporated in the product by the addition of certain substances in large amounts such as weakening or coloring of the fibers and fabrics produced. Such added substances have taken the form of materials producing a characteristic color, materials subject to spectrographic analysis, odorant compounds, and the like.

Heretofore, the use of radioactive materials as an identifying means has not been looked upon with favor, particularly because of the potential dangers from the radiations emanating therefrom. Moreover, if the radioactive materials are short lived, then the value of such a means of identification is minimal. 'If the radioactive compounds have long half-lives, they would be not only dangerous but in most instances would be outlawed. Furthermore, the presence of high energy radiation would affect the base material to be identified, and this cannot be tolerated, especially where the emphasis is on uniformity and constancy of quality which factors are essential. The employment of coloring matter, such as pigments and dyestuffs, as well as odorants such as perfumes, and the like, is at most only slightly better. Duplication of such additives, along with their generally transient existence, contraindicates these techniques for identification.

A method has been discovered whereby products, and particularly synthetic polymers, may be tagged with extremely minute quantities of specific elements, and the latter readily identified at a future time. In view of the very small amounts of tagging" material used, the properties of the base products are completely unaffected, except that it then becomes possible to determine the presence of the tag and thereby identify the product with the source or manufacturer. The tagging materials ememployed in accordance with this invention are completely safe, inert, do not affect subsequent treatments of the base material, and, in spite of the small quantities used, are permanent with respect to the effectiveness thereof.

[It is an important object of the present invention to provide a novel process for tagging substances for subsequent identification thereof.

It is another object of this invention to provide a novel process for improving synthetic polymeric substances to facilitate the determining of the source thereof.

It is still another object of the present invention to provide a process whereby synthetic polymeric materials may be tagged with minute and inexpensive amounts of a substance to provide for the subsequent identification thereof.

It is a further object of this invention to provide a novel process for the tagging of synthetic polymeric materials, and, in particular, nylon in filament and/or yarn form.

Another object of this invention is to provide tagged materials, and, in particular, tagged polymeric materials.

Still another object of this invention is to provide tagged synthetic polymeric materials, especially in filamentary and/ or yarn form.

A further object of the present invention is to provide a novel method of identifying tagged materials, particularly synthetic polymeric materials.

Another object of the present invention is to provide a novel method of determining the presence of tagging elements in synthetic polymeric substances, and particularly in nylon yarns and filaments.

Other objects will appear hereinafter proceeds.

The objects of the present invention are attained by the incorporation into the material to be tagged, said material more particularly and preferably being a synthetic polymeric substance such as polyamides, polyesters, and polyolefins, of a selected metal which is characterized by certain critical properties. The metal must be safe, inert, stable, and effective in extremely minute quantities. It

as the description must not affect the properties of the polymer, whether dyed or undyed; and it must have no undesirable effect on the appearance of the polymer in the filament, yarn or fabric form, whether dyed or undyed. It must be compatible with the material in any of the desired structural forms and must remain at a minimum concentration during the normal processing of the polymer material from the time it is produced from the monomeric form through the usual and conventional treatments normally given to the material thereafter. Such treatments include laundering, scouring, dyeing, heating, cooling, dye-stripping, spinning, weaving, and the like. It is preferred that the metallic substance employed in the process of this invention be readily available to make the entire technique and products economically feasible. It must be capable of identification to the exclusion of possible contaminants and interfering substances.

While many metallic substances, or metals, may at first blush appear to meet the aforementioned prerequisites, most fail based upon the following factors and considerations:

1) The selected metal is already used to perform some other function in combination with the polymeric substance.

(2) The selected metal fails, on closer analysis to meet every requirement set forth above.

(3) The selected metal is being used as a tag with a method of identification not herein contemplated.

(4) The selected metal fails to meet other requirements hereinafter to be described.

With respect to item 1, such metals as manganese and copper are currently being employed to effect the light stabilization of nylon, and therefore could not be used as identifying means.

Many metals do not withstand the rigors of polymer and fiber processing. Still others interfere with the polymerization reaction. These are some examples of item 2 failings.

Some metals are used in relatively large quantities as tags for identification by spectrographic analysis, thereby fail under item 3.

Finally, and perhaps most importantly, most metals are not suitable for identification by the unique method contemplated in the present invention. This method is known as neutron activation analysis. The basic feature of this method lies in converting an inert metal to a radioactive form by bombardment with neutrons, and then measuring the induced radioactivity as a function of the concentration of the metal. The chief recommendation for this method of analysis is the extreme sensitivity which is attainable. Metal concentrations of less than one part per million are quickly, conveniently, and accurately ascertained. Amounts as little as 0.1 part per million can be accurately detected in the polymeric materials contemplated in this invention.

The basic principle behind neutron activation analysis lies in the ability of neutrons to penetrate the nucleus of any element and transform the element into an isotope of increased atomic mass. In many cases these transformations result in unstable or radioactive forms of the element. In such an unstable state, they emit radiation which can be detected by the usual techniques for measuring radioactivity. The nature and energy of the emitted radiation together with the half-life of the activated nuclide are characteristic properties and their measurement can therefore be used to identify and estimate the amount of he active isotope and, consequently, the amount of the inactive metal originally present.

In order to adapt the neutron activation analytical technique for tagging and subsequently identifying polymeric substances, it is necessary that the metal selected as the tag be sufiiciently unique and rare to the extent that it is not normally present in the material to be identified. Where the metal might be present in the material to be identified, but not by choice or design, the amount thereof must be much less (preferably below than the amount used for tagging purposes. Still further, to permit the practical application of the instant method with but trace quantities of tagging metal, the following additional requirements must be met:

(1) A favorable half-life;

(2) The nuclear cross-section of the metal atom; and

(3) The saturation factor.

Item 3 is related to items 1 and 2, and takes into account the fact that as soon as a significant number of nuclei have become activated through neutron capture they undergo radioactive decay at a characteristic rate expressed by the half-life of the activated nuclide.

In selecting the metal to be used for tagging pur poses, and particularly where the selection is a direct function of the minimum amount which can be detected by the method employed in this invention, one must also take into consideration the equipment used for counting the radiations emitted by the decaying isotope and also the neutron flux of the source used for irradiation.

Based on the above factors, it has been determined that concentrations of tagging metals as low as 0.1 part per million of polymer, and in some instances as low as 0.002 part per million, can be detected readily, using a typical neutron source for irradiation, such as a neutron generator or a nuclear reactor. The aforementioned minute metal concentrations not only can be detected, but different metals can be readily discriminated one from the other by the use of appropriate radiation discrimination instruments such as a gamma ray spectrometer. The measurement of the gamma radiation is done with a conventional scintillation detector, e.g., a sodium iodide scintillation crystal; and for beta rays one may employ a Geiger-Mueller tube.

The metals which have been found to meet the requirements outlined above are the following:

Goldatomic weight of 197 (this constitutes of the natural element);

Indiumatomic weight of (this constitutes 95% of the natural element); and

Lanthanum-atomic weight 139 (this constitutes 99.9%

of the natural element) Neutron activation of gold 197 yields radioactive gold 198 with a half-life of 2.7 days; activation of indium 115 yields indium 116 which has a half-life of 54 minutes; and neutron activation of lanthanum 139 gives lanthanum 140 with a half-life of 40 hours.

These metals have sufficiently short half-lives that sufficient activation for detection is reached after relatively short exposures. This fact, coupled with the high abundance of the isotope with the requisite atomic weight, provides for significant and necessary measurable activity.

To illustrate the need for the selected tagging metal to meet each requirement, a comparison with silver, atomic Weight 109, is enlightening. This isotope is present in an amount of 49% of the natural element. It has a nuclear cross-section about the same as gold 197, but the half-life of radioactive silver 110 is 253 days. This results in low measurable activity even after an activation time of 24 hours, and finally approximately 100 times more silver concentration is needed than gold concentration.

The general method for producing the tagged polymers of the present invention involves uniformly distributing the metal in suitable form in the polymer mass. Since uniformity of distribution is essential, it is preferred to add the metal to the polymer precursors. Thus, in the case of nylon 6 (polycaprolactam), the selected metal form can be added to the monomeric caprolactam prior to polymerization. When added prior to polymerization, the metal can be, and preferably is, in soluble form to give a more uniform distribution throughout the product. Subsequent polymerization of the lactam has been found to insolubilize the metal, thereby providing the desired form of the metal in the final product. This effect is probably due to reduction of the metal to its colloidal form by reaction with a negligible amount of the lactam. If, however, the metal is to be added after polymerization, it is most effective when added in the colloidal form. In this state it is most insoluble and least reactive, in contradistinction to the ionic form of the metal which would tend to plate out on contact with metal surfaces and would be more apt to leach out in subsequent treatments of the polymer. It is also possible to employ the metal in the form of an insoluble compound thereof, such as oxide.

Similarly, the addition of the tag metal can be added, in the case of polyester, prior to polymerization in the glycol. For polyolefin type compositions, the identifying metal can be added after polymerization and uniformly dispersed in the polymer.

While the amount of the metal based on the weight of polymer is not necessarily critical, obviously the least amount consistent with accuracy and detectability should be employed. With gold as the metal tag, amounts as low as 0.1 part per million may be used. Using indium, as little as 0.002 part per million may be used; and using lanthanum, one may use as low as about 0.5 part per million. In general, it is preferred to operate at the lowest level of metal concentration detectable for economical reasons.

At any time subsequent to the incorporation of the metal tag into the polymer, it becomes possible to identify the polymer product by exposing a suitable sample, which may be only a few grams of a thin filament or yarn, to a neutron activation source for a sufficient time to induce a significantly measurable activity. Since, as pointed out above, the measurable activity is related to the saturation factor of the nuclide and the latter, in turn, is a function of the neutron flux, the activation time will vary accordingly, depending upon the neutron source. In general, however, at a flux of about l-2 l0 neutrons/ cm. /sec., an exposure of about 30 minutes is sufiicient. Cou-ntings are then made, either immediately with short half-lived indium 116, or after about 24 hours with gold 198 or lanthanum 140. After 24 hours there is only a 23% loss in the gold activity and even after 48 hours the loss is still only 40%. Where manganese is present in the polymer, and gold is the tagging element, it is preferred to Wait 24 hours before counting to permit the resultant radioactive manganese to decay. When the selected metal is indium, the short half-life of the irradiated nuclide does not permit the same type of manipulation. However, by the use of a gamma ray spectrometer, it is possible to dif ferentiate among the principal peaks in the gamma spectra of the interfering metals.

The following examples will serve to illustrate the present invention without being deemed limitative thereof. Parts are by weight unless otherwise indicated.

Example 1 Gold in colloidal form is prepared as follows:

To an aqueous solution of chloroauric acid (0.5 mg. of gold per ml.) there is added sufficient aqueous sodium carbonate for neutralization. A few drops of a 0.1% aqueous tannin solution are added and the mixture is then allowed to stand for several hours at room temperature, whereby a slow reduction of the gold ions to the colloidal form results as evidenced by the formation of a deep purple solution (suspension).

In corporation of gold in and polymerization of caprolactam:

A sufficient quantity of the above-produced gold sol is added to 3,500 g. of molten caprolactam to yield 1 part per million of gold, which is then polymerized in an autoclave in the usual manner using acetic acid as the catalyst and a temperature of about 200 C. The resulting polymer is chipped, washed, and dried.

The polymer is then spun and drawn, and thereafter made into a 70/32 yarn, which is knit into tubes. The knit tubes are given two standard launderings. Samples of the lactam, the chips before washing and the chips after wash ing and drying, along with the samples of the knit tubes before and after laundering, are exposed in a nuclear reactor for 30 minutes at a neutron flux of -1.8 l0 neutrons per cm. per sec. Both beta and gamma counts indicate that but a few percent of the gold content is lost as a result of the aforementioned processing and treatment.

Additional samples of knit tubes are scoured, dyed (using both disperse and acid dye formulations), stripped with caustic and hydrosulphite, and redyed. Similar neutron activation and detection as carried out above indicates substantially no loss in gold content as a result of such diverse processings.

Example 2 To confirm the data obtained in Example 1, the latter is repeated using, however, an equivalent amount of gold tagged with radioactive gold 198. The same results are obtained as in Example 1.

Example 3 The general procedures of Example 1 are again followed except that three separate batches of 50 kilograms of polymer are prepared. One lot is used as a control and contains no added gold; and the other two lots contain 0.1 and 0.25 part, respectively, per million parts polymer of the colloidal gold. The polymer is spun as a 40/ 13 bright yarn. Samples of the yarn from the three lots, along with a sample of polymer chips containing 0. 1 part per million of gold, are activated as in Example 1. The gold contents are found to be in excellent agreement with the amounts added. Two different commercial nylon 6 yarns containing no added gold are also given a similar activation and analysis, and these are found to contain less than 0.001 part per million of gold in relation to the polymer. Gold is found in most natural and synthetic fibers, indicating the ubiquitous nature of the element, but not in amounts which affect the value and accuracy of the techniques and products of the present invention.

Example 4 This example demonstrates that in the low metal concentrations herein contemplated there is no discernible difference in the textile properties of the yarn.

Example 3 is repeated in the preparation of three different yarn lots. A tricot fabric is knitted with the three different yarns, 4-cm. bands of each being repeated in rotation across the cm. width. The fabric is boiled off and divided into three parts. One part is simply heat-set, the second is dyed with Potamine White BT and heat-set, and the third part is dyed with Acid Red by the Lyogen P method and heat-set. No differences are noted among the three yarn lots. On the cones there is also no detectable difference among the three yarn lots.

Example 5 Example 1 is again repeated using in place of 1 part per million of gold the following concentrations:

(a) 0.25 part gold per million parts lactam (b) 0.50 part gold per million parts lactam The results obtained are comparable to those of Example 1.

Example 6 A solution of gold chloride containing 0.20 gram of gold in 50 ml. of water was added to 1000 kilograms of molten caprolactam, which was then polymerized in the usual manner. The resulting polymer was chipped, washed, dried, spun, and drawn as 40/13 yarn. Samples of this yarn were irradiated in a nuclear reactor at a neutron fiux of 1.8x 1 0 neutrons per cm. per second, and the induced radioactivity measured with a multichannel gamma ray spectrometer.

From the data, the gold content of the yarn samples was calculated to be 0.14 to 0.18 part per million by weight, compared to less than 0.001 part per million for yarn to which no gold had been added.

Example 7 Solutions of indium and lanthanum, corresponding to 0.1, 0.5, and 1.0 part indium and 0.5 and 1.0 part lanthanum to one million parts caprolactam, were added to samples of nylon chips and yarn, irradiated, and counted as in Example 1. Successful detection of the above concentrations by gamma ray spectrum analysis indicates that both indium and lanthanum can be employed as a source identifying means for textile yarns. Simple calculations base-d on available neutron flux density and sensitivity of gamma ray analysis indicate that the indium concentration could be lowered to about 0.002 ppm. and still be satisfactory as an identifying means.

The present invention has been illustrated and specifically exemplified in accordance with the foregoing description and examples. It is clear, however, that metal concentrations other than those specifically set forth may be used but within the limits herein disclosed. The specific polymerization technique of Example 1 forms no critical part of this invention, and obviously other methods for polymerizing caprolactam may be employed. Again, while it has been shown as the preferred embodiment that the metal tag be incorporated into the monomer prior to polymer formation, it is also possible to obtain a uniform admixture by other techniques. Thus, one may mix the selected metal, in its selected form, with molten polymer. Both polyester and polyolefin substances may easily be tagged as heretofore pointed out without material alteration in basic procedures applicable to nylon. Other obvious changes and departures from the instant disclosure may be made without, however, departing from the scope of the present invention.

What is claimed is:

1. In a method for the production of shaped articles of a fiber-forming synthetic polymer selected from the group consisting of polyamides, polyesters and polyolefins and whereby such articles are made readily identifiable, the step comprising adding to said polymer or its monomeric precursor at least one material selected from the group of gold, indium and lanthanum and in amounts wherein (a) from about 0.1 to 0.5 part of gold per million parts of polymer, (b) from about 0.002 to about 1 part of indium per million parts of polymer and, (c) from about 0.5 to 1 part of lanthanum per million parts of polymer is used to provide a measurable radioactivity upon neutron activation of the said material.

2. Process of claim 1 wherein the polyamide is polycaprolactam.

3. Process of claim 1 wherein the polyester is polyethylene terephthalate.

4. Process of claim 1 wherein the polyolefin is polypropylene.

5. As an article of manufacture, a shaped article consisting of a synthetic fiber-forming polymeric material selected from the group of polyamides, polyesters and polyolefins containing trace amounts of a metal selected from the group consisting of gold, indium and lanthanum, said amounts ranging, on a weight basis,

(a) from about 0.1 to 0.5 part of gold per million parts of polymeric material,

(b) from about 0.00:2 to about 1 part of indium per million parts of polymeric material; and

(c) from about 0.5 to about 1 part of lanthanum per million parts of said polymeric material.

References Cited UNITED STATES PATENTS 2,671,250 3/1954 Fidell 25071 X 2,993,258 7/1961 Spunt 250-1 06 X 3,002,091 9/ 1961 Armstrong 25083 3,115,576 12/1963 Rickard 250-435 3,227,881 1/ 1966 Gordon 250-106 FOREIGN PATENTS 898,398 6/1962 Great Britain.

RALPH G. NILSON, Primary Examiner.

r SAUL ELBAUM, Assistant Examiner.

U.S. Cl. X.R. 250-83 

